One of the most common problems during the height of the
canning season is the incidence of jar breakage. I feel bad that many work so
hard to grow or pay for ingredients only to find them floating in the water
when they take the lid off the canner. Here are several reasons that canning jars will break.

There are occasionally
defective jars in a new box. Manufacturing isn’t always perfect and sometimes
there will be a bad batch but for Ball/Kerr made here in America it’s cyclical
and usually winds up being in one region of the country. There are other makers
of canning jars such as Mainstay and even Better Homes and Garden which until last year were being sold at Walmart. Mainstay jars, made in China, have had the most issues of
late, but as I said a defective new jar can happen once and awhile and really no manufacturers
are free of breakage issues.

Using Commercial jars for canning; Reusing or recycling
pasta, mayonnaise, jelly, baby food or any commercial jars are highly susceptible
to breakage. These jars should NOT be used unless the Ball two piece lid/ring fits on them and should only be used for water bath canning. They are not stored the same way as canning jars and are not protected in the stores against clinking and knocking into other jars. Note: Prego Pasta Sauce jars should not ever be used since they put a plastic coating on the jars and the manufacturer has stated not to reuse for canning.

Another reason may be the home canner using a metal knife to remove the bubbles
in the jars. You can scratch the glass and over time create stress fractures
that eventually will cause the jar to break. Some of those breaks look like the bottom of the jar just falling out in a perfect circle.

Toss that butter knife
aside and use a either a small rubber spatula, Bubble and Headspace measurer (shown below) or find a great set of
chopsticks since they get through some of those tight spaces.

One of the more common factors is the change in
temperature for the glass. We heat the jars either by water bath canner or dishwasher to introduce "hot jars" into the hot
water of the canner. As they cool during filling, the change in temperature
when adding the jars back to the water bath can cause breakage. To help avoid
excessive cooling make sure that you use a dishtowel on your counter to keep a
barrier between the cold surface and the hot glass.

Rings tied together to make a rack!

Make sure there is a rack on the bottom of the canning pot because the heat, directly on the
jar, causes breakage. This is not as common but it does happen when we are
not paying attention or when you are new to canning. A rack keeps the direct
heat of the stove away from the bottoms of the jars. This can be accomplished inexpensively by
tying a set of rings together.

Some of the older jars that we pick up at yard sales and thrift shops, ones that get donated, or passed down from family may have hairline cracks that are difficult to see. Some even get these crack going through the dishwasher or being washed in the sink. It's rare but they do occasionally break. It is advised that if you have older jars to only use them in a water bath to keep them from being over stressed.

These are some of the ways that I have seen or investigated breaks during canning and processing. It can happen in one or two in a canning season, but using some of the tips that I mentioned above may help avoid loss of your work in "canner error".

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Altitude Adjustments

The gel point method is also noted in many cookbooks and is a process to test the gel of a jam, jelly or preserve. There are two methods of testing using a spoon or a plate.

SHEET TEST

Dip a cold metal spoon into the boiling soft spread. Lift the spoon and hold it horizontally with edge down so that the syrup runs off the edge. As the mixture cooks, the drops will become heavier and will drop off the spoon separately but two at a time. When the two drops join together and “sheet” off the spoon, the gel stage has been reached.

FREEZER TEST

Chill a small saucers in the freezer. Place a teaspoonful of soft spread on the chilled saucer and place in the freezer for 1 minute. Remove the saucer from the freezer and push the edge of the spread with your finger. A mixture that has reached the gel stage will be set, and the surface will wrinkle when the edge is pushed.